Evaluating the Bioactivity of a Novel Antimicrobial and Anticancer Peptide, Dermaseptin-PS4(Der-PS4), from the Skin Secretion of Phyllomedusa sauvagii

Amphibian-Derived Natural Anticancer Peptides and Proteins: Mechanism of Action, Application Strategies, and Prospects

Cancer is one of the major diseases that seriously threaten human life. Traditional anticancer therapies have achieved remarkable efficacy but have also some unavoidable side effects. Therefore, more and more research focuses on highly effective and less-toxic anticancer substances of natural origin. Amphibian skin is rich in active substances such as biogenic amines, alkaloids, alcohols, esters, peptides, and proteins, which play a role in various aspects such as anti-inflammatory, immunomodulatory, and anticancer functions, and are one of the critical sources of anticancer substances. Currently, a range of natural anticancer substances are known from various amphibians. This paper aims to review the physicochemical properties, anticancer mechanisms, and potential applications of these peptides and proteins to advance the identification and therapeutic use of natural anticancer agents.

Discovery of new 1,4-disubstituted 1,2,3-triazoles: in silico ADME profiling, molecular docking and biological evaluation studies

In this work, eight new 1,2,3-triazoles (6a-h) were synthesized from acetylenes' "click" reaction with p-substituted azide derivatives. The structures of the compounds were characterized using standard analytical and spectroscopic methods (elemental analysis, FT-IR, ¹H(¹³C)NMR). The anticancer, antioxidant, α-amylase, ADME, molecular docking studies of synthesized triazoles were investigated. According to α -amylase enzyme inhibition results, all compounds except 6c (IC₅₀: 2299 μg/mL) were found to have a higher IC₅₀ value than the standard drug acarbose (IC₅₀: 891 μg/mL). Compound 6g (IC₅₀: 68 μg/mL) exhibited 13 times higher activity than standard acarbose. All compounds, except 6e, have been shown to have greater DPPH radical scavenging capabilities than BHT and β-carotene standards. According to ABTS radical scavenging studies, all compounds showed higher scavenging activity than ascorbic acid and Trolox. To determine the anticancer activity of the synthesized compounds, they were screened against the Hela cell line, and the results were compared with standard cisplatin (IC₅₀: 16.30 μg/mL). Compound 6a (IC₅₀: 49.03 μg/mL) was determined to have moderate activity relative to cisplatin. The compounds were examined comprehensively for ADME characteristics and did not violate any drug-likeness rule. ADME data showed that all physicochemical and pharmacological parameters of the compounds remained within defined limits as specified in Lipinski's rules (RO5) and put forth a high bioavailability profile. The molecular docking findings show that all molecules have a high affinity by exhibiting polar and apolar contact with essential residues in the binding pocket of α-amylase.Communicated by Ramaswamy H. Sarma.

Bioactive compounds: a goldmine for defining new strategies against pathogenic bacterial biofilms?

Most human infectious diseases are caused by microorganisms growing as biofilms. These three-dimensional self-organized communities are embedded in a dense matrix allowing microorganisms to persistently inhabit abiotic and biotic surfaces due to increased resistance to both antibiotics and effectors of the immune system. Consequently, there is an urgent need for novel strategies to control biofilm-associated infections. Natural products offer a vast array of chemical structures and possess a wide variety of biological properties; therefore, they have been and continue to be exploited in the search for potential biofilm inhibitors with a specific or multi-locus mechanism of action. This review provides an updated discussion of the major bioactive compounds isolated from several natural sources - such as plants, lichens, algae, microorganisms, animals, and humans - with the potential to inhibit biofilm formation and/or to disperse established biofilms by bacterial pathogens. Despite the very large number of bioactive products, their exact mechanism of action often remains to be clarified and, in some cases, the identity of the active molecule is still unknown. This knowledge gap should be filled thus allowing development of these products not only as novel drugs to combat bacterial biofilms, but also as antibiotic adjuvants to restore the therapeutic efficacy of current antibiotics.

Triazole based novel molecules as potential therapeutic agents: Synthesis, characterization, biological evaluation, in-silico ADME profiling and molecular docking studies

In this study, eight new compounds (7a-h) based on triazole compounds containing ester groups were synthesized with high yields. The structures of the synthesized compounds (7a-h) were elucidated by various spectroscopic methods (element analysis, FT-IR, ¹H-(¹³C) NMR). Antioxidant, anticancer, and α-amylase enzyme inhibition activities of synthesized new triazole derivatives were carried out, and the effects of different groups on the activity were investigated. When the determined antioxidant properties of the compounds were examined, all synthesized compounds showed a moderate radical scavenging effect against radicals depending on the concentration (6.25-200 g/mL). All compounds except the three derivatives were found to have higher IC₅₀ values than the standard drug acarbose (IC₅₀: 891 μg/mL) according to the α-amylase enzyme inhibition results. Compound 7g (IC₅₀: 50 g/mL) was discovered to have nearly eighteen (18) times the activity of the conventional medication acarbose (IC₅₀: 891 μg/mL). Compounds synthesized for anticancer activity studies were screened against the Hela cell line, and the results were compared with standard cis-platinum (IC₅₀: 16.30 μg/mL). Compound 7g (IC₅₀: 19.78 μg/mL) was found to have almost the same activity as cis-platinum. Using Qikprop, the compounds were thoroughly tested for ADME qualities, and none violated any drug similarity standards. According to ADME data, whole physicochemical drug-likeness parameters of molecules remained within defined ranges as stipulated in the Lipinski rules (RO5) and revealed a high bioavailability profile. The molecular docking results with 2QV4 and 4GQR alpha-amylase enzymes demonstrated that all molecules have a high affinity, indicating polar and apolar interaction with critical amino acids in the α-amylase binding pocket.

Recent Advances in Multifunctional Antimicrobial Peptides as Immunomodulatory and Anticancer Therapy: Chromogranin A-Derived Peptides and Dermaseptins as Endogenous versus Exogenous Actors

Antimicrobial peptides (AMPs) are produced by all living organisms exhibiting antimicrobial activities and representing the first line of innate defense against pathogens. In this context, AMPs are suggested as an alternative to classical antibiotics. However, several researchers reported their involvement in different processes defining them as Multifunctional AMPs (MF-AMPs). Interestingly, these agents act as the endogenous responses of the human organism against several dangerous stimuli. Still, they are identified in other organisms and evaluated for their anticancer therapy. Chromogranin A (CgA) is a glyco-phosphoprotein discovered for the first time in the adrenal medulla but also produced in several cells. CgA can generate different derived AMPs influencing numerous physiological processes. Dermaseptins (DRSs) are a family of α-helical-shaped polycationic peptides isolated from the skin secretions of several leaf frogs from the Phyllomedusidae family. Several DRSs were identified as AMPs and, until now, more than 65 DRSs have been classified. Recently, these exogenous molecules were characterized for their anticancer activity. In this review, we summarize the role of these two classes of MF-AMPs as an example of endogenous molecules for CgA-derived peptides, able to modulate inflammation but also as exogenous molecules for DRSs, exerting anticancer activities.

In Vitro & In Vivo Studies on Identifying and Designing Temporin-1CEh from the Skin Secretion of Rana chensinensis as the Optimised Antibacterial Prototype Drug

Amphibian skin secretion is an ideal source of antimicrobial peptides that are difficult to induce drug resistance to due to their membrane-targeting mechanism as a new treatment scheme. In this study, a natural antimicrobial peptide Temporin-1CEh was identified by molecular cloning and mass spectrometry from the skin secretions of the Chinese forest frog (Rana chensinensis). Through the study of the structure and biological activity, it was found that Temporin-1CEh was a helical peptide from the Temporin family, and possessed good anti-Gram-positive bacteria activity through the mechanism of membrane destruction. Seven analogues were further designed to obtain broad-spectrum antimicrobial activity and higher stability in different physiological conditions. The results showed that T1CEh-KKPWW showed potent antibacterial activity with significantly increasing the activity against Gram-negative bacteria in vitro and in vivo with low haemolysis. In addition, T1CEh-KKPWW2 showed high sensitivity to the pH, serum or salts conditions, which applied a branched structure to allow the active units of the peptide to accumulate. Even though the haemolytic activity was increased, the stable antibacterial activity made this novel analogue meet the conditions to become a potential candidate in future antimicrobial and antibiofilm applications.

Exploration of the Structure-Function Relationships of a Novel Frog Skin Secretion-Derived Bioactive Peptide, t-DPH1, through Use of Rational Design, Cationicity Enhancement and In Vitro Studies

Amphibian skin-derived antimicrobial peptides (AMPs) have attracted increasing attention from scientists because of their excellent bioactivity and low drug resistance. In addition to being the alternative choice of antibiotics or anticancer agents, natural AMPs can also be modified as templates to optimise their bioactivities further. Here, a novel dermaseptin peptide, t-DPH1, with extensive antimicrobial activity and antiproliferative activity, was isolated from the skin secretion of Phyllomedusa hypochondrialis through 'shotgun' cloning. A series of cationicity-enhanced analogues of t-DPH1 were designed to further improve its bioactivities and explore the charge threshold of enhancing the bioactivity of t-DPH1. The present data suggest that improving the net charge can enhance the bioactivities to some extent. However, when the charge exceeds a specific limit, the bioactivities decrease or remain the same. When the net charge achieves the limit, improving the hydrophobicity makes no sense to enhance bioactivity. For t-DPH1, the upper limit of the net charge was +7. All the designed cationicity-enhanced analogues produced no drug resistance in the Gram-negative bacterium, Escherichia coli. These findings provide creative insights into the role of natural drug discovery in providing templates for structural modification for activity enhancement.

Indole-3-propionic acid, a tryptophan-derived bacterial metabolite, increases blood pressure via cardiac and vascular mechanisms in rats

Recent evidence suggests that gut bacteria-derived metabolites interact with the cardiovascular system and alter blood pressure (BP) in mammals. Here, we evaluated the effect of indole-3-propionic acid (IPA), a gut bacteria-derived metabolite of tryptophan, on the circulatory system. Arterial BP, electrocardiographic, and echocardiographic (ECHO) parameters were recorded in male, anesthetized, 12-wk-old Wistar-Kyoto rats at baseline and after intravenous administration of either IPA or vehicle. In additional experiments, rats were pretreated with prazosin or pentolinium to evaluate the involvement of the autonomic nervous system in cardiovascular responses to IPA. IPA's concentrations were measured using ultra-high performance liquid chromatography tandem mass spectrometry. The reactivity of endothelium-intact and -denuded mesenteric resistance arteries was tested. Cells' viability and lactate dehydrogenase (LDH) cytotoxicity assays were performed on cultured cardiomyocytes. IPA increased BP with a concomitant bradycardic response but no significant change in QTc interval. The pretreatment with prazosin and pentolinium reduced the hypertensive response. ECHO showed increased contractility of the heart after the administration of IPA. Ex vivo, IPA constricted predilated and endothelium-denuded mesenteric resistance arteries and increased metabolic activity of cardiomyocytes. IPA increases BP via cardiac and vascular mechanisms in rats. Furthermore, IPA increases cardiac contractility and metabolic activity of cardiomyocytes. Our study suggests that IPA may act as a mediator between gut microbiota and the circulatory system.

Evaluating the effect of dermaseptin S4 and its derivatives on multidrug-resistant bacterial strains and on the colon cancer cell line SW620

Dermaseptins are peptides found in the skin secretions of Phyllomedusinae frogs. These peptides exert a lytic action on various microorganisms and have no considerable hemolytic effect except dermaseptin S4 (DS4) which exhibits a powerful cytotoxic effect. Therefore, we synthesized several analogs of DS4 in an attempt to find molecules with a weak hemolytic effect and significant bioactivities. In this study, we performed the synthesis of truncated peptides by introducing C-terminal and N-terminal amino acid deletions of the native sequence. All peptide analogs, in comparison with parental peptide, were tested firstly on human red blood cells to work out their cytotoxicity, secondly on the multidrug-resistant bacteria by trying to find MICs, and finally on colon cancer tumor cell line SW620 using the MTT test so as to investigate the anti-proliferative effect. Our results showed that, on the one hand, the N terminus of the native peptide was necessary for the antibacterial activity and the anti-proliferative effect of the peptide. On the other hand, the hemolytic activity was more notable in the sequences broken down on the C-terminal side.

Brevinin-1GHd: a novel Hylarana guentheri skin secretion-derived Brevinin-1 type peptide with antimicrobial and anticancer therapeutic potential

Host-defense antimicrobial peptides (AMPs) from amphibians are usually considered as one of the most promising next-generation antibiotics because of their excellent antimicrobial properties and low cytotoxicity. In the present study, one novel Brevinin-1 type peptide, Brevinin-1GHd, was isolated and characterized from the skin secretion of the frog, Hylarana guentheri. Brevinin-1GHd was found to possess a wide range of antimicrobial activity through penetrating the bacterial membrane within a short time while showing low hemolysis at bactericidal concentrations, even against the resistant strains. It also inhibited and eradicated biofilms that are thought to be closely related to the rise in resistance. Meanwhile, Brevinin-1GHd exhibited wide-spectrum anti-proliferation activity toward human cancer lines. Taken together, these results indicate that Brevinin-1GHd with its excellent antimicrobial and anticancer activities is a promising candidate for a novel antibiotic agent, and study of its structure–activity relationships also provided a rational template for further research and peptide analog design.

Identification and Target-Modification of SL-BBI: A Novel Bowman-Birk Type Trypsin Inhibitor from Sylvirana latouchii

The peptides from the ranacyclin family share similar active disulphide loop with plant-derived Bowman-Birk type inhibitors, some of which have the dual activities of trypsin inhibition and antimicrobial. Herein, a novel Bowman-Birk type trypsin inhibitor of the ranacyclin family was identified from the skin secretion of broad-folded frog (Sylvirana latouchii) by molecular cloning method and named as SL-BBI. After chemical synthesis, it was proved to be a potent inhibitor of trypsin with a Ki value of 230.5 nM and showed weak antimicrobial activity against tested microorganisms. Modified analogue K-SL maintains the original inhibitory activity with a Ki value of 77.27 nM while enhancing the antimicrobial activity. After the substitution of active P1 site to phenylalanine and P2' site to isoleucine, F-SL regenerated its inhibitory activity on chymotrypsin with a Ki value of 309.3 nM and exhibited antiproliferative effects on PC-3, MCF-7 and a series of non-small cell lung cancer cell lines without cell membrane damage. The affinity of F-SL for the β subunits in the yeast 20S proteasome showed by molecular docking simulations enriched the understanding of the possible action mode of Bowman-Birk type inhibitors. Further mechanistic studies have shown that F-SL can activate caspase 3/7 in H157 cells and induce apoptosis, which means it has the potential to become an anticancer agent.

Ferritin Nanocages for Protein Delivery to Tumor Cells

The delivery of therapeutic proteins is one of the greatest challenges in the treatment of human diseases. In this frame, ferritins occupy a very special place. Thanks to their hollow spherical structure, they are used as modular nanocages for the delivery of anticancer drugs. More recently, the possibility of encapsulating even small proteins with enzymatic or cytotoxic activity is emerging. Among all ferritins, particular interest is paid to the Archaeoglobus fulgidus one, due to its peculiar ability to associate/dissociate in physiological conditions. This protein has also been engineered to allow recognition of human receptors and used in vitro for the delivery of cytotoxic proteins with extremely promising results.

Dermaseptins, Multifunctional Antimicrobial Peptides: A Review of Their Pharmacology, Effectivity, Mechanism of Action, and Possible Future Directions

Dermaseptins are a group of α-helical shaped polycationic peptides isolated from the Hylid frogs, with antimicrobial effects against bacteria, parasites, protozoa, viruses in vitro. Besides, anti-tumor effects have been demonstrated. However, few animal experiments and no clinical trials have been conducted thus far. This review summarizes the current knowledge on the pharmacology, ethno pharmacology, effectivity against infectious pathogens and tumors cells and the mechanism of action of the Dermaseptins. Future research should focus on further clarification of the mechanisms of action, the effectivity of Dermaseptins against several cancer cell lines and their applicability in humans.

Design of N-Terminal Derivatives from a Novel Dermaseptin Exhibiting Broad-Spectrum Antimicrobial Activity against Isolates from Cystic Fibrosis Patients

Dermaseptins are an antimicrobial peptide family widely identified from the skin secretions of phyllomeudusinae frogs. Here, we identify Dermaseptin-PC (DM-PC), from the skin secretion of Phyllomedusa coelestis, and further investigate the properties of this peptide, and a number of rationally designed truncated derivatives. The truncated 19-mer derived from the N-terminus exhibited similar antimicrobial potency when compared to the parent peptide, but the haemolytic effect of this truncated peptide was significantly decreased. Based on previous studies, the charge and hydrophobicity of truncated derivatives can affect the bioactivity of these peptides and thus we designed a 10-mer derivative with an optimised positive charge and a cyclohexylalanine (Cha) at the C-terminus for enhancing the hydrophobicity, DMPC-10A, which retained the antimicrobial activity of the parent peptide. To further investigate the influence of Cha at the C-terminus on activity, it was substituted by alanine (Ala) to generate another derivative, DMPC-10, but this was found to be much less potent. In addition, DM-PC, DMPC-19 and DMPC-10A not only rapidly killed planktonic bacteria isolated from cystic fibrosis (CF) patient, but also effectively eradicated their biofilm matrices.

A Novel Dermaseptin Isolated from the Skin Secretion of Phyllomedusa tarsius and Its Cationicity-Enhanced Analogue Exhibiting Effective Antimicrobial and Anti-Proliferative Activities

A novel dermaseptin peptide, dermaseptin-PT9 (DPT9), was isolated and identified from Phyllomedusa tarsius by the combination of molecular cloning and LC-MS analysis. Chemically synthesised DPT9 was broadly effective against the tested microorganisms through the disruption of cell membranes and showed weak haemolytic activity towards horse erythrocytes. It also exhibited anti-proliferative effect against various human cancer cells. Moreover, an analogue with enhanced cationicity, K^{8, 23}-DPT9, in which Asp⁸ and Glu²³ were substituted by lysine residues, had a markedly increased antimicrobial effect against all tested microorganisms and disrupted microbial cell membranes. This analogue also showed no haemolysis at its effective antimicrobial concentrations. In addition, K^{8, 23}-DPT9 displayed an enhanced anti-proliferative effect against cancer cells, while displayed weak activity against the normal human cell line, HMEC-1.